Metering of catalysts

ABSTRACT

To meter catalysts into a reactor, the catalyst is firstly suspended in a hydrocarbon in a reservoir and the suspension obtained is kept in motion by stirring and then fed via a three-way metering valve and an ejector into the actual reactor, wherein the suspension containing the catalyst is firstly discharged from the reservoir by means of a pump and continuously circulated by returning the suspension via the three-way metering valve within a closed piping system to the reservoir, subsequently setting a pressure in the reservoir which is from 0.1 to 30 bar higher than the pressure in the reactor and then continuously introducing the suspension into the reactor via a flow meter which controls the three-way metering valve and via a downstream ejector by pulse operation of the now open three-way metering valve.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the U.S. national stage under 35 U.S.C. §371 ofInternational Application PCT/EP02/00919, filed Jan. 30, 2002, claimingpriority to German Patent Application No. 101 05 276.6, filed Feb. 2,2001; the disclosures of International Application PCT/EP02/00919 andGerman Patent Application No. 101 05 276.6, each as filed, areincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a method of metering catalysts into areactor, where the catalyst is firstly suspended in a hydrocarbon in areservoir and the suspension obtained is kept in motion by stirring andthen fed via a three-way metering valve and an ejector into the actualreactor, wherein the suspension containing the catalyst is firstlydischarged from the reservoir by means of a pump and continuouslycirculated by returning the suspension via the three-way metering valvewithin a closed piping system to the reservoir, subsequently setting apressure in the reservoir which is from 0.1 to 30 bar higher than thepressure in the reactor and then continuously introducing the suspensioninto the reactor via a flow meter which controls the three-way meteringvalve and via a downstream ejector by pulse operation of the now openthree-way metering valve.

The present invention further provides an apparatus for meteringcatalysts which is suitable, inter alia, for the polymerization ofC₂-C₂₀-olefins.

BACKGROUND OF THE INVENTION

Polymers of C₂-C₂₀-olefins can be prepared by liquid-phasepolymerization, by polymerization in the monomer (bulk polymerization),by suspension polymerization or by polymerization from the gas phase.The polymerization is usually carried out with the aid of aZiegler-Natta catalyst which customarily comprises a titanium-containingsolid component, an organic aluminum compound and an organic silanecompound (EP-B 45 977, EP-A 171 200, U.S. Pat. Nos. 4,857,613,5,288,824). Polymers of C₂-C₂₀-olefins can, however, also be obtained bypolymerization with the aid of metallocene compounds orpolymerization-active metal complexes. An important aspect here is thatthe catalyst used is metered into the polymerization reactor in anefficient manner.

The known techniques for metering finely-divided catalysts for thepreparation of polyolefins have mostly been established for decades.Many of these techniques do not take account of catalyst developmentswhich have taken place. Thus, modern high-performance catalysts requireparticular homogeneity of metering even in the case of small amounts.The development of metallocene catalysts has also made it necessary forfully or partially active catalysts to be introduced into the process ina safe and reliable manner.

Current and established techniques of metering catalysts arepredominantly based on a portioning device which via an appropriateconveying means feeds a particular volume element into the reactor.

Examples which may be mentioned are the methods described in EP-A 0 025137 and in U.S. Pat. No. 4,690,804, in which a dimple feeder ordouble-check feeder takes portions of a sedimented suspension of thecatalyst from a reservoir and, by rotation through 180°, passes it to atransport stream which conveys the suspension into the reactor. Thedisadvantage of this method is the fixed volume of the feeder. This hasthe consequence that at low outputs or high catalyst productivity thenumber of doses per hour is very low and the process can thus easily beupset. In addition, in the case of catalysts having a high activity,there is the risk that the catalyst will not be sufficiently quicklydistributed homogeneously in the reactor, which can quickly lead to lumpformation when the catalyst activity is high. A further disadvantage ofmetering a sedimented catalyst suspension is that the catalystconcentration decreases as the fill level of the metering vessel dropsand the setting of the portioning device therefore has to be adjustedcontinually.

A further example of a metering method is that described, inter alia, inDE-A 22 57 669. Here, the catalyst is blown into the reactor by means ofnitrogen. However, this method has the disadvantage that substantialquantities of nitrogen get into the reactor and reduce the partialpressure of the monomers; they can thus have an adverse effect on theactivity and the efficiency of the catalyst system.

A further possibility is to meter the catalyst into the reactor via alock system as described in U.S. Pat. No. 3,827,830 or U.S. Pat. No.4,123,601. However, experience has shown that such lock systems, forexample systems having ball valves, are difficult to operate reliablyover a prolonged period in conjunction with inorganic materials. Typicalwear phenomena are, inter alia, leaks and blocked valves. This isassociated with increased maintenance requirements and high costs. Thesemetering methods, too, convey the material in portions, with theabovementioned disadvantages.

DE-A 30 26 816 describes the metering of a catalyst suspension from astock zone into a mixing zone via a valve. Constructions of this typetend to become blocked, particularly when the valve is open forprolonged periods. Controlled metering of defined amounts is thus notpossible on a long-term basis. A mixing zone as described in thisapplication is not suitable for metering activated or partiallyactivated catalysts since deposit formation frequently occurs.

It is an object of the present invention to remedy the disadvantagesindicated and to develop a new method of metering catalysts into areactor, by means of which the catalyst used can be introducedcontinuously and very homogeneously into the reactor. The metering ofthe catalyst should occur so that very few impurities are carried intothe reactor and so that the amount of catalyst metered in is measurable.Furthermore, the method of the present invention should be able to becarried out using a metering system which is largely free of movingparts having large sealing areas, since experience has shown thatpronounced wear occurs in such places and can have an adverse effect onoperational reliability and operating life.

We have found that this object is achieved by a new, significantlyimproved method of metering catalysts into a reactor, where the catalystis firstly suspended in a hydrocarbon in a reservoir and the suspensionobtained is kept in motion by stirring and then fed via a three-waymetering valve and an ejector into the actual reactor, wherein thesuspension containing the catalyst is firstly discharged from thereservoir by means of a pump and continuously circulated by returningthe suspension via the three-way metering valve within a closed pipingsystem to the reservoir, subsequently setting a pressure in thereservoir which is from 0.1 to 30 bar higher than the pressure in thereactor and then continuously introducing the suspension into thereactor via a flow meter which controls the three-way metering valve andvia a downstream ejector by pulse operation of the now open three-waymetering valve.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is an illustrative flow diagram of the polymerization process.

DESCRIPTION OF THE INVENTION

The method of the present invention is preferably used for meteringcatalysts for the polymerization of C₂-C₂₀-olefins. C₂-C₂₀-Olefins whichcan be used are, in particular, aliphatic C₂-C₂₀-alk-1-enes,particularly preferably C₂-C₁₀-alk-1-enes such as ethylene, propylene,1-butene, 1-pentene, 1-hexene, 1-heptene or 1-octene, especiallyethylene, propylene or 1-butene. Furthermore, the term C₂-C₂₀-olefins asused in the context of the present invention also encompasses, inparticular, internal C₄-C₂₀-olefins such as 2-butene or isoprene,C₄-C₂₀-dienes such as 1,4-butadiene, 1,5-hexadiene, 1,9-decadiene,5-ethylidene-2-norbornene, 5-methylidene-2-norbornene, also cyclicolefins such as norbornene or α-pinene or else trienes such as1,6-diphenyl-1,3,5-hexatriene, 1,6-di-tert-butyl-1,3,5-hexatriene,1,5,9-cyclododecatriene, trans,trans-farnesol, and also polyunsaturatedfatty acids or fatty acid esters. The process is suitable for preparinghomopolymers of C₂-C₂₀-olefins or copolymers of C₂-C₂₀-olefins with,preferably, up to 30% by weight of other copolymerized olefins having upto 20 carbon atoms. For the purposes of the present invention,copolymers include both random copolymers and block or high-impactcopolymers.

The method of the present invention is particularly useful for meteringcatalysts in the preparation of homopolymers of propylene or copolymersof propylene with up to 30% by weight of other copolymerized olefinshaving up to 10 carbon atoms. The copolymers of propylene may be randomcopolymers or block or high-impact copolymers. If the copolymers ofpropylene have a random structure, they generally contain up to 15% byweight, preferably up to 6% by weight, of other olefins having up to 10carbon atoms, in particular ethylene, 1-butene or a mixture of ethyleneand 1-butene.

The block or high-impact copolymers of propylene are polymers in which apropylene homopolymer or a random copolymer of propylene with up to 15%by weight, preferably up to 6% by weight, of other olefins having up to10 carbon atoms is prepared in a first stage and a propylene-ethylenecopolymer which has an ethylene content of from 5 to 99% by weight andmay further comprise additional C₄-C₁₀-olefins is then polymerized ontoit in the second stage. In general, the amount of propylene-ethylenecopolymer polymerized on in the second stage is such that the copolymerproduced in the second stage makes up from 3 to 90% by weight of the endproduct.

Catalysts which can be used are, inter alia, Phillips catalysts based onchromium compounds or Ziegler catalysts. The method of the presentinvention is also suitable, inter alia, for metering Ziegler-Nattacatalyst systems, in particular catalyst systems comprising not only atitanium-containing solid component a) but also cocatalysts in the formof organic aluminum compounds b) and optionally electron donor compoundsc).

However, Ziegler-Natta catalyst systems based on metallocene compoundsor polymerization-active metal complexes can also be metered by means ofthe method of the present invention.

Titanium compounds used for preparing the titanium-containing solidcomponent a) are generally the halides or alkoxides of trivalent ortetravalent titanium. Titanium alkoxide halide compounds or mixtures ofvarious titanium compounds are also suitable. Preference is given tousing those titanium compounds containing chlorine as halogen.Preference is likewise given to titanium halides which consist of onlytitanium and halogen, especially titanium chlorides and in particulartitanium tetrachloride.

The titanium-containing solid component a) preferably comprises at leastone halogen-containing magnesium compound. For the present purposes,halogens are chlorine, bromine, iodine and fluorine, with preferencebeing given to bromine or, in particular, chlorine. Thehalogen-containing magnesium compounds can either be used directly inthe preparation of the titanium-containing solid component a) or beformed during its preparation. Magnesium compounds which are suitablefor preparing the titanium-containing solid component a) are especiallymagnesium halides, in particular magnesium dichloride or magnesiumdibromide, or magnesium compounds from which the halides can be obtainedin a customary manner, e.g. by reaction with halogenating agents, forexample magnesium alkyls, magnesium aryls, magnesium alkoxy compounds ormagnesium aryloxy compounds or Grignard compounds. Preferred examples ofhalogen-free compounds of magnesium which are suitable for preparing thetitanium-containing solid component a) are n-butylethylmagnesium orn-butyloctylmagnesium. Preferred halogenating agents are chlorine andhydrogen chloride. However, the titanium halides can also serve ashalogenating agents.

In addition, the titanium-containing solid component a) advantageouslycomprises electron donor compounds, for example monofunctional orpolyfunctional carboxylic acids, carboxylic anhydrides or carboxylicesters, also ketones, ethers, alcohols, lactones or organophosphorus ororganosilicon compounds.

As electron donor compounds within the titanium-containing solidcomponent, preference is given to using carboxylic acid derivatives andin particular phthalic acid derivatives of the formula (II)

where X and Y are each a chlorine or bromine atom or a C₁-C₁₀-alkoxyradical or together represent oxygen in an anhydride function.Particularly preferred electron donor compounds are phthalic esters inwhich X and Y are each a C₁-C₈-alkoxy radical.

Examples of preferred phthalic esters are diethyl phthalate, di-n-butylphthalate, diisobutyl phthalate, di-n-pentyl phthalate, di-n-hexylphthalate, di-n-heptyl phthalate, di-n-octyl phthalate anddi-2-ethylhexyl phthalate.

Further preferred electron donor compounds within thetitanium-containing solid component are aliphatic or cycloaliphaticdiethers or else diesters of 3- or 4-membered, substituted orunsubstituted cycloalkane-1,2-dicarboxylic acids, and also monoesters ofsubstituted benzophenone-2-carboxylic acids or substitutedbenzophenone-2-carboxylic acids. As hydroxy compounds for forming theseesters, use is made of the alkanols customary in esterificationreactions, for example C₁-C₁₅-alkanols or C₅-C₇-cycloalkanols, which mayin turn bear one or more C₁-C₁₀-alkyl groups, and also C₆-C₁₀-phenols.

It is also possible to use mixtures of various electron donor compounds.

In the preparation of the titanium-containing solid component a), use isgenerally made of from 0.05 to 2.0 mol, preferably from 0.2 to 1.0 mol,of the electron donor compounds per mole of magnesium compound.

In addition, the titanium-containing solid component a) may compriseinorganic oxides as supports. In general, a finely divided inorganicoxide which has a mean particle diameter of from 5 to 200 μm, preferablyfrom 10 to 70 μm, is used as support. Here, the mean particle diameteris the volume-based mean (median) of the particle size distributiondetermined by Coulter counter analysis.

The particles of the finely divided inorganic oxide are preferablycomposed of primary particles having a mean particle diameter of from 1to 20 μm, in particular from 1 to 5 μm. The primary particles areporous, granular oxide particles which are generally obtained by millinga hydrogel of the inorganic oxide. It is also possible to sieve theprimary particles before they are processed further.

Furthermore, the inorganic oxide which is preferably used also has voidsand channels having a mean diameter of from 0.1 to 20 μm, in particularfrom 1 to 15 μm, and having a macroscopic proportion by volume of thetotal particle in the range from 5 to 30%, in particular in the rangefrom 10 to 30%.

The mean particle diameters of the primary particles and the macroscopicproportion by volume of the voids and channels of the inorganic oxideare advantageously determined by image analysis using scanning electronmicroscopy or electron probe microanalysis, in each case on particlesurfaces and particle cross sections of the inorganic oxide. Themicrographs obtained are evaluated and the mean particle diameters ofthe primary particles and the macroscopic proportion by volume of thevoids and channels are determined therefrom. Image analysis ispreferably carried out by converting the electron-microscopic datamaterial into a halftone binary image and digital evaluation by means ofa suitable EDP program, e.g. the software package Analysis from SIS.

The inorganic oxide which is preferably used can be obtained, forexample, by spray drying the milled hydrogel, which for this purpose ismixed with water or an aliphatic alcohol. Such finely divided inorganicoxides are also commercially available.

Furthermore, the finely divided inorganic oxide usually has a porevolume of from 0.1 to 10 cm³/g, preferably from 1.0 to 4.0 cm³/g, and aspecific surface area of from 10 to 1000 m²/g, preferably from 100 to500 m²/g. The values specified here are the values determined by mercuryporosimetry in accordance with DIN 66133 and by nitrogen adsorption inaccordance with DIN 66131, respectively.

It is also possible to use an inorganic oxide whose pH, i.e. thenegative logarithm to the base ten of the proton concentration, is inthe range from 1 to 6.5, in particular in the range from 2 to 6.

Suitable inorganic oxides are, in particular, the oxides of silicon,aluminum, titanium or one of the metals of main groups I and II of thePeriodic Table. Particularly preferred oxides are aluminum oxide,magnesium oxide, sheet silicates and especially silicon oxide (silicagel). It is also possible to use mixed oxides such as aluminum silicatesor magnesium silicates.

The inorganic oxides used as supports have water present on theirsurface. This water is partly physically bound by adsorption and partlychemically bound in the form of hydroxyl groups. The water content ofthe inorganic oxide can be reduced or completely eliminated by thermalor chemical treatment. In a chemical treatment, use is generally made ofcustomary desiccants such as SiCl₄, chlorosilanes or aluminum alkyls.The water content of suitable inorganic oxides is from 0 to 6% byweight. Preference is given to using an inorganic oxide in the form inwhich it is commercially obtainable, without further treatment.

The magnesium compound and the inorganic oxide are preferably present inthe titanium-containing solid component a) in such amounts that from 0.1to 1.0 mol, in particular from 0.2 to 0.5 mol, of the compound ofmagnesium is present per mole of inorganic oxide.

Furthermore, C₁-C₈-alkanols such as methanol, ethanol, n-propanol,isopropanol, n-butanol, sec-butanol, tert-butanol, isobutanol,n-hexanol, n-heptanol, n-octanol or 2-ethylhexanol or mixtures thereofare generally used in the preparation of the titanium-containing solidcomponent a). Preference is given to using ethanol.

The titanium-containing solid component can be prepared by methods knownper se. Examples of such methods are described, inter alia, in EP-A 45975, EP-A 45 977, EP-A 86 473, EP-A 171 200, GB-A 2 111 066, U.S. Pat.Nos. 4,857,613 and 5,288,824. The process known from DE-A 195 29 240 ispreferably employed.

Suitable aluminum compounds b) include not only trialkylaluminums butalso compounds of the type in which an alkyl group is replaced by analkoxy group or by a halogen atom, for example by chlorine or bromine.The alkyl groups may be identical or different. Linear or branched alkylgroups are possible. Preference is given to using trialkylaluminumcompounds whose alkyl groups each have from 1 to 8 carbon atoms, forexample trimethylaluminum, triethylaluminum, triisobutylaluminum,trioctylaluminum or methyldiethylaluminum or mixtures thereof.

Apart from the aluminum compound b), electron donor compounds c) such asmonofunctional or polyfunctional carboxylic acids, carboxylic anhydridesor carboxylic esters, also ketones, ethers, alcohols, lactones andorganophosphorus and organosilicon compounds are generally used asfurther cocatalyst. The electron donor compounds c) can be identical toor different from the electron donor compounds used for preparing thetitanium-containing solid component a). Preferred electron donorcompounds here are organosilicon compounds of the formula (I)R¹ _(n)Si(OR²)_(4-n)  (I)where R¹ are identical or different and are each a C₁-C₂₀-alkyl group, a5- to 7-membered cycloalkyl group which may in turn be substituted byC₁-C₁₀-alkyl, a C₆-C₁₈-aryl group or a C₆-C₁₈-aryl-C₁-C₁₀-alkyl group,R² are identical or different and are each a C₁-C₂₀-alkyl group and n is1, 2 or 3. Particular preference is given to compounds in which R¹ is aC₁-C₈-alkyl group or a 5- to 7-membered cycloalkyl group and R² is aC₁-C₄-alkyl group and n is 1 or 2.

Among these compounds, particular mention may be made ofdimethoxydiisopropylsilane, dimethoxyisobutylisopropylsilane,dimethoxydiisobutylsilane, dimethoxydicyclopentylsilane,dimethoxyisopropyl-tert-butylsilane, dimethoxyisobutyl-sec-butylsilaneand dimethoxyisopropyl-sec-butylsilane.

The cocatalysts b) and c) are preferably used in such amounts that theatomic ratio of aluminum from the aluminum compound b) to titanium fromthe titanium-containing solid component a) is from 10:1 to 800:1, inparticular from 20:1 to 200:1, and the molar ratio of the aluminumcompound b) to the electron donor compound c) is from 1:1 to 250:1, inparticular from 10:1 to 80:1.

The titanium-containing solid component a), the aluminum compound b) andthe generally used electron donor compound c) together form theZiegler-Natta catalyst system. The catalyst constituents b) and c) canbe introduced into the reactor together with the titanium-containingsolid component a) or as a mixture or individually in any order andsubjected to activation there.

The method of the present invention can also be employed for meteringZiegler-Natta catalyst systems based on metallocene compounds orpolymerization-active metal complexes into the reactor.

For the present purposes, metallocenes are complexes of transitionmetals with organic ligands, which together with compounds capable offorming metallocenium ions give active catalyst systems. For metering bythe method of the present invention, the metallocene complexes aregenerally present in supported form in the catalyst system. Supportsused are frequently inorganic oxides. Preference is given to theabove-described inorganic oxides which are also used for preparing thetitanium-containing solid component a).

Customarily used metallocenes contain titanium, zirconium or hafnium ascentral atoms, with zirconium being preferred. In general, the centralatom is bound via a n bond to at least one, generally substituted,cyclopentadienyl group and to further substituents. The furthersubstituents can be halogens, hydrogen or organic radicals, withpreference being given to fluorine, chlorine, bromine or iodine or aC₁-C₁₀-alkyl group.

Preferred metallocenes contain central atoms which are bound via two πbonds to two substituted cyclopentadienyl groups, with particularpreference being given to those in which substituents of thecyclopentadienyl groups are bound to both cyclopentadienyl groups. Veryparticular preference is given to complexes whose cyclopentadienylgroups are additionally substituted by cyclic groups on two adjacentcarbon atoms.

Further preferred metallocenes are ones which contain only onecyclopentadienyl group which is, however, substituted by a radical whichis also bound to the central atom.

Examples of suitable metallocene compounds are

-   ethylenebis(indenyl)zirconium dichloride,-   ethylenebis(tetrahydroindenyl)zirconium dichloride,-   diphenylmethylene-9-fluorenylcyclopentadienylzirconium dichloride,-   dimethylsilanediylbis(3-tert-butyl-5-methylcyclopentadienyl)-zirconium    dichloride,-   dimethylsilanediylbis(2-methylindenyl)zirconium dichloride,-   dimethylsilanediylbis(2-methylbenzindenyl)zirconium dichloride-   dimethylsilanediylbis(2-methyl-4-phenylindenyl)zirconium dichloride,-   dimethylsilanediylbis(2-methyl-4-naphthylindenyl)zirconium    dichloride,-   dimethylsilanediylbis(2-methyl-4-isopropylindenyl)zirconium    dichloride and-   dimethylsilanediylbis(2-methyl-4,6-diisopropylindenyl)zirconium

dichloride and also the corresponding dimethylzirconium compounds.

The metallocene compounds are either known or are obtainable by knownmethods.

The metallocene catalyst systems further comprise compounds capable offorming metallocenium ions. Suitable compounds are strong, unchargedLewis acids, ionic compounds containing Lewis-acid cations or ioniccompounds having Brönsted acids as cation. Examples aretris(pentafluorophenyl)borane, tetrakis(pentafluorophenyl)borate orsalts of N,N-dimethylanilinium. Further suitable compounds capable offorming metallocenium ions are open-chain or cyclic aluminoxanecompounds. These are usually prepared by reacting trialkylaluminums withwater and are generally in the form of mixtures of both linear andcyclic chain molecules of various lengths.

In addition, the metallocene catalyst systems may compriseorganometallic compounds of the metals of main groups I, II and III ofthe Periodic Table, e.g. n-butyllithium, n-butyl-n-octylmagnesium ortriisobutylaluminum, triethylaluminum or trimethylaluminum.

The method of the present invention can be used for metering catalystswhich are usually used in the polymerization of C₂-C₂₀-olefins. Thepolymerization can be carried out in at least one reaction zone,frequently in two or more reaction zones connected in series (reactorcascade), in the gas phase, in the liquid phase, in a slurry or in bulk.The reaction conditions in the actual polymerization can also be set sothat the respective monomers are present in two different phases, forexample partly in the liquid state and partly in the gaseous state(condensed mode).

It is possible to use the customary reactors employed for thepolymerization of C₂-C₂₀-olefins. Suitable reactors are, for example,continuously operated horizontal or vertical stirred vessels,circulation reactors, loop reactors, multistage reactors orfluidized-bed reactors or else combinations of the abovementionedreactor technologies. The size of the reactors is not of criticalimportance for applicability of the method of the present invention. Itdepends on the output which is to be achieved in the reaction zone or inthe individual reaction zones.

The method of the present invention can, however, also be used formetering catalysts into reactors in which the reaction carried out isnot a polymerization but instead another organic or inorganic reaction,for example an oxidation reaction or a hydrogenation reaction.

In particular, reactors used are fluidized-bed reactors or horizontallyor vertically stirred powder bed reactors. The reaction bed can comprisethe polymer of C₂-C₂₀-olefins which is produced in the respectivereactor.

According to a particularly preferred embodiment of the method of thepresent invention, the reaction is carried out in a reactor or in acascade of reactors connected in series in which the pulverulentreaction bed is kept in motion by means of a vertical stirrer.Particularly useful stirrers of this type are free-standing helicalstirrers. Such stirrers are known, for example, from EP-B 000 512 andEP-B 031 417. These reactors distribute the pulverulent reaction bedparticularly uniformly. Examples of such pulverulent reaction beds aredescribed in EP-B 038 478. The reactor cascade preferably comprises twotank-shaped reactors which are connected in series and are each providedwith a stirrer and have a capacity of from 0.1 to 100 m³, for example12.5, 25, 50 or 75 m³.

According to the method of the present invention for metering catalystsinto reactors, the catalyst, for example the titanium-containing solidcomponent in the case of Ziegler-Natta catalysts or the metallocenecompound in the case of metallocene catalysts, is firstly suspended in ahydrocarbon in a reservoir. Suitable reservoirs are, inter alia, stirredvessels provided with a stirrer. Hydrocarbons which can be used are, inparticular, aliphatic, aromatic or else olefinic C₃-C₃₀-hydrocarbons ormixtures of these. Particularly suitable hydrocarbons are, inter alia,hexane, heptane, isodecane or white oil or benzene, toluene orethylbenzene, also linear or branched C₂-C₂₀-α-olefins such as 1-butene,1-pentene, propylene or hexene. A particularly suitable suspensionmedium is, for example, white oil, namely a liquid mixture of saturated,aliphatic hydrocarbons.

The suspension obtained in this way is kept in motion by means ofsuitable stirrers, for example by means of anchor stirrers or bladestirrers. Particularly suitable stirrers include Viscoprop stirrers fromEkato. The stirrer speed is usually from 5 to 300 revolutions perminute, in particular from 10 to 150 revolutions per minute.

The catalyst-containing suspension is discharged from the reservoir bymeans of an appropriate pump and continuously circulated by beingconveyed via the three-way metering valve within a closed piping systemback into the reservoir. Pumps suitable for this purpose are, forexample, displacement pumps or diaphragm pumps. Particularly well suitedpumps are, inter alia, Cerex diaphragm pumps from Bran & Luebbe inNorderstedt. It is advisable to circulate the volume in the reservoirfrom 0.1 to 5 times, preferably from 0.5 to 2 times, per hour. Thecirculation is preferably monitored by means of a mass flow meter. Forthis purpose, it is possible to use, inter alia, mass flow meters of thetrade name Promass from Endress & Hausser. The catalyst-containingsuspension is metered into the reactor by firstly setting, by means ofthe three-way metering valve, a pressure in the reservoir which is from0.1 to 30 bar, in particular from 0.5 to 15 bar, higher than thepressure in the reactor. The three-way metering valves used for thispurpose preferably have only one plug (e.g. type 187037-/P, specialconstruction type from Kaemmer).

Subsequently, by means of pulse operation of the now open three-waymetering valve, the suspension is introduced continuously into thereactor via a flow meter which controls the three-way metering valve andvia a downstream ejector. The catalyst-containing suspension is meteredby pulse operation of the three-way metering valve which in the “open”position is open to a degree of from 1 to 100%, preferably from 10 to100%, for a freely selectable time of preferably from 1 to 600 seconds,more preferably from 1 to 100 seconds. In the “closed” position, thethree-way metering valve is open to a degree of from 0 to 100%,preferably from 0 to 10%, for a freely selectable time of preferablyfrom 1 to 600 seconds, in particular from 1 to 100 seconds.

The amount of catalyst-containing suspension which has been metered inthis way flows through a flow meter, preferably a “Promass instrumentfrom Endress & Hausser, to check the amount of catalyst being metered.The three-way metering valve can be controlled by means of the outputsignal from the flow meter and the metering of the catalyst can thus beregulated in a closed loop. The catalyst-containing suspension isfinally fed via an ejector into the reactor. Here, it may be advisablefor an aliphatic or olefinic hydrocarbon, for example propylene, to beconveyed into the ejector.

Subsequently, the cocatalysts, for example the aluminum compound b) andthe electron donor compounds c) in the case of Ziegler-Natta catalystsor the cocatalysts used in the case of metallocene catalysts, e.g.triethylaluminum or triisobutylaluminum, are firstly introduced into thereactor and, after addition of the appropriate monomers, the actualchemical reaction, for example the polymerization of the C₂-C₂₀-olefins,is then carried out.

The polymerization can be carried out under customary reactionconditions, preferably at from 40 to 150° C. and pressures of from 1 to100 bar. Preference is given to temperatures of from 40 to 120° C., inparticular from 60 to 100° C., and pressures of from 10 to 50 bar, inparticular from 15 to 40 bar. The molar mass of the C₂-C₂₀-olefinpolymers formed can be controlled and set by addition of regulatorscustomary in polymerization technology, for example hydrogen. Apart fromsuch molar mass regulators, it is also possible to use activityregulators, i.e. compounds which influence the catalyst activity, orantistatics. The latter prevent deposit formation on the reactor wall asa result of electrostatic charging. The C₂-C₂₀-olefin polymers generallyhave a melt flow rate (MFR) of from 0.1 to 4000 g/10 min, in particularfrom 0.2 to 200 g/10 min, at 230° C. under a weight of 2.16 kg. The meltflow rate corresponds to the amount of polymer pressed out of the testapparatus standardized in accordance with ISO 1133 over a period of 10minutes at 230° C. and under a weight of 2.16 kg. Particular preferenceis given to polymers whose melt flow rate is from 2 to 80 g/10 min, at230° C. under a weight of 2.16 kg.

The mean residence times in the reaction to which the method of thepresent invention is applied are in the customary ranges. The residencetimes in the polymerization of C₂-C₂₀-olefins are in the range from 0.1to 10 hours, preferably in the range from 0.2 to 5 hours and inparticular in the range from 0.3 to 4 hours.

The catalyst-metering apparatus which is likewise provided by thepresent invention is shown in FIG. 1 below. The apparatus preferablycomprises a reservoir (1) in which the catalyst is suspended in ahydrocarbon and which is provided with a suitable stirrer and, connectedthereto, a piping system provided with a pump (2) by means of which thecontents of the reservoir are circulated and a three-way metering valve(4) which is connected via a further piping system provided with a flowmeter (5) to an ejector (6) via which the suspension comprising thecatalyst is fed into the reactor (7), for example by means of propylene.

It may be advisable for the piping system which circulates the contentsof the reservoir in the apparatus of the present invention to beadditionally provided with a mass flow meter (3).

The method of the present invention and the apparatus likewise providedby the present invention make it possible to introduce catalysts, forexample for the polymerization of C₂-C₂₀-olefins, continuously and veryhomogeneously into a reactor, with virtually no interfering impuritiesbeing carried in and, in addition, the amount of catalyst metered inbeing measurable. The method of the present invention also has a highoperational reliability and can be operated for a long time.

Various types of catalysts for, inter alia, the polymerization ofC₂-C₂₀-olefins can be metered into reactors by means of the method ofthe present invention or the apparatus of the present invention. Theresulting homopolymers, copolymers or mixtures of such polymers areparticularly suitable for producing films, fibers or moldings.

EXAMPLES

Examples 1, 2, 3 and 5 and Comparative Examples A to C and E werecarried out using a Ziegler-Natta catalyst system comprising atitanium-containing solid component a) prepared by the following method.

In a first step, a finely divided silica gel having a mean particlediameter of 30 μm, a pore volume of 1.5 cm³/g and a specific surfacearea of 260 m²/g was admixed with a solution of n-butyloctylmagnesium inn-heptane, using 0.3 mol of the magnesium compound per mole of SiO₂. Thefinely divided silica gel additionally had a mean particle size of theprimary particles of 3-5 μm and had voids and channels which had adiameter of 3-5 μm and a macroscopic proportion by volume of the totalparticle of about 15%. The mixture was stirred at 95° C. for 45 minutesand then cooled to 20° C., after which 10 times the molar amount, basedon the organomagnesium compound, of hydrogen chloride was passed intothe mixture. After 60 minutes, the reaction product was admixed with 3mol of ethanol per mole of magnesium while stirring continually. Thismixture was stirred at 80° C. for 0.5 hour and subsequently admixed with7.2 mol of titanium tetrachloride and 0.5 mol of di-n-butyl phthalate,in each case per 1 mol of magnesium. The mixture was subsequentlystirred at 100° C. for 1 hour, and the solid obtained in this way wasfiltered off and washed a number of times with ethylbenzene.

The resulting solid product was extracted at 125° C. with a 10% strengthby volume solution of titanium tetrachloride in ethylbenzene for 3hours. The solid product was then separated from the extractant byfiltration and washed with n-heptane until the washings contained only0.3% by weight of titanium tetrachloride.

The titanium-containing solid component a) comprised

3.5% by weight of Ti

7.4% by weight of Mg

28.2% by weight of Cl.

In addition to the titanium-containing solid component a),triethylaluminum and organic silane compounds were used as cocatalysts,in a manner similar to the teachings of U.S. Pat. Nos. 4,857,613 and5,288,824.

Example 1

A 100 l stirred vessel was charged with a 15% by weight suspension ofthe titanium-containing solid component a) in white oil (Winog 70). Thissuspension was circulated at a rate of 100 kg per hour via the attachedpump. The three-way metering valve connected in the circuit was operatedusing an open time of 4 seconds at 45% and a closed time of 1 second at0%. The amount of suspension metered in this way was conveyed via a flowmeter and fed by means of an ejector operated by 240 kg/h of propyleneinto a continuously operated 12.5 m³ polymerization reactor. A pressurewhich was 8.5 bar higher than that in the polymerization reactor wasapplied to the stirred vessel.

In addition, 0.3 kg of triethylaluminum per metric ton of freshpropylene (0.3 kg/t of fresh propylene) and 0.1 kg ofisobutylisopropyldimethoxysilane per metric ton of fresh propylene andhydrogen as molar mass regulator in an amount of 110 g per metric ton offresh propylene were metered into the polymerization reactor. Propyleneand ethylene were subsequently polymerized under the conditions, i.e.temperature and pressure, indicated in Table I at an average residencetime of 1.8 hours. The particle size distribution of thepropylene-ethylene copolymer obtained, together with the standarddeviations for the parameters pressure and temperature, are shown inTable I below.

Example 2

The procedure of Example 1 was repeated, but a higher pressure and ahigher temperature were employed.

Comparative Example A

A 100 l stirred vesssel was charged with a 15% by weight suspension ofthe titanium-containing solid component in white oil (Winog 70). Thecatalyst was fed downward by means of a double check feeder installed atthe bottom outlet of the vessel using a pause time of 80 seconds (closedposition) and a metering time of 3 seconds (metering position) andconveyed into the reactor by means of 240 kg/h of propylene. Thepolymerization conditions correspond to those of Example 1. It can beseen from the data in Table I that the reaction parameters (cf. standarddeviations) are subject to significantly greater fluctuations and thepolymer morphology is significantly coarser.

Comparative Example B

The procedure of Comparative Example A was repeated, but thepolymerization was carried out at 28 bar and 77° C. Over a period ofthree hours, the particle morphology became very coarse (more than 5% ofparticles >4 mm), so that the experiment had to be stopped.

Example 3

The polymerization was carried out as described in Example 1, but noethylene was introduced.

Comparative Example C

The polymerization was carried out as described in Comparative ExampleA, but no ethylene was introduced and the pressure and temperature werealtered. This experiment, too, shows that significantly greaterfluctuations are found in the process when using the conventionalmethod.

Example 4

The procedure of Example 1 according to the present invention wasrepeated, but a metallocene catalyst comprisingrac-dimethylsilanediylbis(2-methylbenzo[e]indenyl)zirconium dichloridesupported on silica gel was used in place of the titanium-containingsolid component a) and no organic silane was introduced. In addition, 20g of isopropanol per metric ton of fresh propylene were metered in.

Comparative Example D

The procedure of Comparative Example A was repeated, but the metallocenecatalyst of Example 4 was used and no silane was introduced. 20 g ofhydrogen per metric ton of fresh propylene were metered in. Onlypropylene was polymerized. The resulting propylene polymer displayed anincreased proportion of coarse particles in the screening unit (particlesize >4 mm).

Comparative Example E

A 100 l stirred vessel was charged with a 15% by weight suspension ofthe titanium-containing solid component a) in white oil (Winog 70). Thecatalyst-containing suspension was conveyed downward via a valveinstalled at the bottom outlet of the stirred vessel without priorcirculation using a pause time of 2 seconds at the setting 0% and ametering time of 10 seconds at a setting of 90%. Underneath this outlet,a mixture of propylene and ethylene was polymerized under the sameconditions as in Example 1. After the valve became blocked and had to becleaned after less than 10 minutes, the experiment was stopped.

Example 5

Example 3 was repeated under analogous conditions, but the catalyst wassuspended in propylene instead of white oil.

Table I below shows the respective pressure, the respective temperatureand the amounts of monomer(s) used in the polymerization for Examples 1,2, 3, 4 and 5 according to the present invention and for ComparativeExamples A, C and D. The table also shows the respective standarddeviations for pressure and temperature and the particle sizedistribution of the polymers obtained, determined by sieve analysis.

TABLE I Experiment No. Ex. 1 Ex. 2 Comp. Ex. A Ex. 3 Comp. Ex. C Ex. 4Comp. Ex. D Ex. 5 Pressure (bar) 24.00 28.00 24.00 30.00 30.00 24.0024.00 30.00 Standard deviation of pressure (bar) 0.72 0.78 0.89 0.550.74 0.45 0.52 0.54 Temperature (° C.) 72.00 77.00 72.00 80.00 80.0067.00 67.00 80.00 Standard deviation of temperature (° C.) 1.36 0.536.01 0.82 3.16 0.30 0.35 0.73 Amount of propylene (kg/h) 1500.00 1500.001500.00 1800.00 1800.00 1800.00 1800.00 1800.00 Amount of ethylene(kg/h) 24.00 24.00 24.00 0 0 0 0 0 Particle size distribution >4 mm 00.10 0.10 0 0 0 0.50 0 >3.15 mm 0.20 0.20 0.60 0 0 0 0.10 0 >2 mm 12.402.70 13.20 0.60 6.70 6.10 4.90 0.80 >1 mm 50.80 37.30 53.00 30.90 44.5068.80 40.10 33.70 >0.5 mm 23.20 41.50 20.80 43.40 30.60 23.50 46.0040.30 >0.25 mm 8.70 14.90 7.70 17.40 11.80 1.60 8.10 17.50 >0.125 mm3.20 2.90 3.50 5.60 4.70 0 0.30 7.00 >0.06 mm 1.4 0.40 1.10 1.80 1.30 00 0.70 >0.04 mm 0.1 0 0 0.30 0.30 0 0 0 <0.04 mm 0 0 0 0 0.10 0 0 0

1. A method of metering catalysts into a reactor, where the catalyst isfirstly suspended in a hydrocarbon in a reservoir and the suspensionobtained is kept in motion by stirring and then fed via a three-waymetering valve and an ejector into the actual reactor, wherein thesuspension containing the catalyst is firstly discharged from thereservoir by means of a pump and continuously circulated by returningthe suspension via the three-way metering valve within a closed pipingsystem to the reservoir, subsequently setting a pressure in thereservoir which is from 0.1 to 30 bar higher than the pressure in thereactor and then continuously introducing the suspension into thereactor via a flow meter which controls the three-way metering valve andvia a downstream ejector by pulse operation of the now open three-waymetering valve.
 2. A method as claimed in claim 1, wherein the contentsof the entire reservoir are circulated from 0.1 to 5 times per hour bymeans of a pump.
 3. A method as claimed in claim 1, wherein thecirculation of the contents of the entire reservoir is monitored bymeans of a mass flow meter.
 4. A method as claimed in claim 1, whereinthe pressure set in the reservoir is from 0.5 to 15 bar higher than thepressure in the reactor.
 5. A method as claimed in claim 1, whereinpropylene is conveyed continuously into the ejector.
 6. A method asclaimed in claim 1 by means of which Ziegler-Natta catalysts based on atitanium-containing solid component are metered into the reactor.
 7. Amethod as claimed in claim 1 by means of which catalysts based on metalcomplexes are fed into the reactor.
 8. A method as claimed in claim 1used for metering catalysts for the polymerization of C₂-C₂₀-olefins. 9.A method as claimed in claim 1 used for metering catalysts for thepolymerization of aliphatic C₂-C₁₀-alk-1-enes.
 10. A method as claimedin claim 1, wherein the catalyst is suspended in a linear or branchedC₂-C₂₀-α-olefin.
 11. A method as claimed in claim 1, wherein thecatalyst is suspended in propylene.